Tag: isotopes and nuclear chemistry

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Questions Related to isotopes and nuclear chemistry

Multiple choice chemistry nuclear physics nuclear reactor the nuclear power station isotopes and nuclear chemistry

The amount of $U ^ { 235 }$ in kg which is to be used per hour in a nuclear reactor of capacity $100$ ($E = 200 MeV/fission$)

  1. $0.45 \times 10^{-5}$
  2. $4.5 \times 10^{-5}$
  3. $4.5 \times 10^{5}$
  4. $45 \times 10^{-5}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Power = 100 MW = 10^8 J/s. Energy per fission = 200 MeV = 3.2 * 10^-11 J. Fissions per second = 10^8 / (3.2 * 10^-11) = 3.125 * 10^18. Mass per second = (3.125 * 10^18 * 235) / (6.022 * 10^23) = 1.22 * 10^-3 g/s. Multiplying by 3600 seconds gives the hourly rate.

Multiple choice chemistry nuclear physics nuclear reactor the nuclear power station isotopes and nuclear chemistry

Cadmium rods are used as moderators in a nuclear reactor.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
Cadmium rods are used in a nuclear reactor for regulating the power level of the reactor. Cadmium rods are used in nuclear reactors to control the fission rate of radioactive material used. It is capable of absorbing many neutrons without fissioning themselves.
Heavy water, graphite etc. are used as moderator
Multiple choice chemistry nuclear physics nuclear reactor the nuclear power station isotopes and nuclear chemistry

An atomic power nuclear reactor can deliver $300$ MW. The energy released due to fission of each nucleus of uranium atom $U^{235} $ is $170$ MeV. The number of uranium atoms fissioned per hour will be 

  1. $4\times 10^{22}$
  2. $30\times 10^{22}$
  3. $10\times 10^{20}$
  4. $5\times 10^{15}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Total energy released per second is 300 MW, which equals 300 x 10^6 J/s. Dividing this by the energy per fission in joules gives the total number of fissions per second, and multiplying by 3600 yields the number of fissions per hour, approximately 4 x 10^22.

Multiple choice chemistry nuclear physics nuclear reactor the nuclear power station isotopes and nuclear chemistry

The fission of one uranium nucleus releases energy of amount x joules. Find the number of fissions required to produced energy at the rate of v MW for t hours a nuclear power plant.

  1. $ \dfrac {yt}{x} $
  2. $ \dfrac{x}{yt} $
  3. $ 3.6 \times 10^9 \dfrac {yt}{x} $
  4. $ 3.6 \times 10^9 \dfrac {x}{yt} $
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Total energy required = Power (v MW) * time (t hours). Total energy = v * 10^6 * t * 3600 Joules. Number of fissions = Total energy / energy per fission (x). This results in the expression involving v, t, and x.

Multiple choice chemistry nuclear physics nuclear reactor the nuclear power station isotopes and nuclear chemistry

During a nuclear fission reaction 

  1. a heavy nucleus breaks into two fragments by itself

  2. a light nucleus bombared by thermal neutrons breaks up

  3. a heavy nucleus bombared by thermal neutrons breaks up

  4. two light nuclei combine to give a heavier nucleus and possibly other products
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
In nuclear physics and nuclear chemistry, nuclear fission is either a nuclear reaction or a radioactive decay process in which the nucleus of an atom splits into smaller parts, and reaction is triggered by neutron bombardment.
Multiple choice chemistry nuclear physics nuclear reactor the nuclear power station isotopes and nuclear chemistry

The fissionable material used in a breeder reactor is ________

  1. $ _{92}\textrm{U}^{235}$
  2. $ _{94}\textrm{Pu}^{239}$
  3. $ _{90}\textrm{Th}^{234}$
  4. $ _{c}\textrm{C}^{12}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Non-fissionable uranium-238 is 140 times more abundant than the fissionable U-235 and can be efficiently converted into Pu-239 by the neutrons from a fission chain reaction.

Multiple choice chemistry nuclear physics nuclear reactor the nuclear power station isotopes and nuclear chemistry

The critical mass of $U^{235}$ can be reduced by 

  1. putting a neutron reflector around it

  2. heating it

  3. mixing impurity in it

  4. putting neutron absorber around it
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
Surrounding a spherical critical mass with a neutron reflector further reduces the mass needed for criticality. A common material for a neutron reflector is beryllium metal. This reduces the number of neutrons which escape the fissile material, resulting in increased reactivity.